Curcuma longa (curcuma, turmeric) is a plant of the ginger plant family (Zigimberaceae), the roots and rhizome of which are used as dye and spice on account of the intense yellow color and the characteristic taste. A variety of biological effects are described for the dried rhizome and extracts therefrom, including stimulation of gastric juice production, anticancer, antioxidative and anti-inflammatory effect. Curcuma longa is traditionally used in Ayurvedic medicine, inter alia in topical applications for skin disorders.
The biological effect of Curcuma longa and extracts therefrom is generally attributed to the presence of curcuminoids, in particular curcumin, demethoxycurcumin and bisdemethoxycurcumin (cf. Jayaprakasha et al., J. Agric. Food Chem. 2002, 50(13), 3668-3672; Sharma, Biochemical Pharmacology 1976, 25(15), 1811-1812 and U.S. Pat. No. 5,861,415), to which are attributed, besides the antioxidative effect, e.g., anti-inflammatory, antibacterial (Negi et al., J. Agric. Food Chem. 1999, 47(10), 4297-4300), antifungal (Apisariyakul et al., Journal of Ethnopharmacology 1995, 49(3), 163-169), antiparasitic, antimutagenic, anticancer (cf. e.g., Ruby et al., Cancer Letters 1995, 94(1), 79-83; Soudamini et al., Indian Journal of Pharmacology 1988, 20 (2-4), 95-101) and detoxifying properties.
One characteristic property of Curcuma longa extracts is the intense yellow color which is caused inter alia by the curcuminoids. Curcuminoids are derived from the curcumin structure
where the substitution pattern on the aromatic rings can vary. Beside curcumin, the best known representatives are demethoxycurcumin
and bisdemethoxycurcumin

On account of the very intense coloring ability, curcumin is also used as food dye (E100).
On account of the described bioactive effects, curcuminoid-containing extracts, obtained from e.g., Curcuma longa, are interesting candidates for active ingredients for topical applications, in particular in cosmetic formulations. However, the intense yellow/orange color stands in the way of one such use; even in concentrations of 0.1% by mass, it causes a significant, unacceptable coloring of creams or lotions.
Kim et al. describe the reduction in the color intensity of Curcuma aromatica and Curcuma longa extracts through irradiation with gamma radiation (Radiation Physics and Chemistry 2006, 75(3), 449-452). The described process is not suitable for the preparation of cosmetic raw materials since treatment with ionizing radiation is generally not accepted by the market.